1. Field of the Invention
Implementations of various technologies described herein generally relate to methods and systems for modeling synthetic seismograms.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Seismic data signals are typically acquired by measuring and recording data during a seismic survey. A seismic survey may be performed by repeatedly firing an impulsive seismic energy source at the surface of the earth, sea or seafloor and recording the received signals at a set of receivers. The receivers may typically be situated at the same surface as the source, but laterally displaced on regular grid positions. However, there may be situations where a non-regular distribution of the receivers is preferred or where the source and the receivers may be positioned at different depth levels. In a typical seismic survey, the source and the receivers may be displaced at fixed intervals (e.g., 25 meters) and in a certain direction (e.g., the “inline” direction).
During the seismic survey, the cycle of firing the source and recording the received signals may be repeated a plurality of times. When firing the seismic source, a pressure wave may be excited and propagated into the subsurface. The pressure wave reflects off interfaces between various earth layers (such as rock, sand, shale, and chalk layers) and propagates upwardly to the set of receivers, where the particle velocity of the wave vibrations or the pressure oscillations of the wave may be measured and recorded.
The strength of the reflected wave is proportional to the amount of change in elastic parameters, e.g., density, pressure velocity, and shear velocity, at the respective interfaces. Consequently, the data recorded by the receivers represents the elastic characteristics of the subsurface below the receivers.
The seismic survey provides a seismogram that can be used to model images of the subsurface. Images of the subsurface may be derived by determining a velocity model of the subsurface. The velocity model is determined within a recursive process that generates synthetic seismograms, and compares the synthetic seismograms to the seismogram from the survey. The velocity model is updated until the synthetic seismogram is similar to the actual survey seismogram.
The synthetic seismogram may be generated as numerous reconstructed wavefronts. The reconstructed wavefronts may be 3-dimensional models of the pressure wave as the pressure wave travels through the subsurface. Typically, the reconstructed wavefronts are modeled using polygon triangulation.